The tallest tree in the Styx Valley stands higher than the Sydney Opera House and in the last election campaign the Prime Minister promised to protect 18,700 hectares of Styx and Florentine Valley trees.

But only about a third of that amount has been protected.

And Federal Forestry Minister Eric Abetz says this promise hasn't been met because the Government was also trying to keep its promise on jobs.

In Hobart, Felicity Ogilvie reports.

FELICITY OGILVIE: The Prime Minster's forestry policy won the Coalition two marginal northern Tasmanian seats at the last federal election.

John Howard travelled to Launceston to tell forest workers he'd protect Tasmania's forests and their jobs.

JOHN HOWARD: I am advised by the industry that no jobs will be threatened by the decisions in relation to strengthening the reserve system that I'll be announcing this afternoon.

FELICITY OGILVIE: That was 2004. Since then, the Government has only protected about a third of the amount of forest it promised to conserve in the Florentine Forest and the Styx Valley.

The Federal Forestry Minister, Senator Eric Abetz, says the Government has protected 14,500 more hectares of forest elsewhere in Tasmania.

Senator Abetz says the decision not to conserve as much of the Florentine Forest and the Styx Valley was made to protect forestry jobs.

ERIC ABETZ: We are unapologetically supportive of our forest industry and our forest workers to ensure that their livelihoods are protected, just as much as we are concerned to protect large tracts of old growth.

FELICITY OGILVIE: Tasmanian Greens Senator, Christine Milne, says because of that broken promise old growth forests are being cut down.

Both forests border Tasmania's massive World Heritage Area.

CHRISTINE MILNE: Now the logging is so bad that the effect of it is influencing the World Heritage Area and the World Heritage Committee, at its global meeting in New Zealand later this year, will consider what the Australian Government is doing with regard to logging that eastern boundary of the Tasmanian Wilderness World Heritage Area.

Gunns wants to build its mill north of Launceston, pulping three million tonnes of woodchips a year.

Gunns, in its application to the State Government, proposes at start up 80 per cent of the woodchips will come from Tasmania's native forests, the rest will be plantation timber.

The Wilderness Society's Geoff Law is unhappy that Gunns will get most of its woodchips from native forests in Tasmania's northeast.

GEOFF LAW: Some of the logging operations up there have to be seen to be believed, and they will be intensified if this mill goes ahead.

So, we have seen mountain-sides scalped, very, very steep slopes with erodable soils, which have been completely cleared of all trees. So species such as the Wedge-tailed Eagle, for example, will almost certainly be driven towards local extinction if that mill goes ahead.

FELICITY OGILVIE: But the head of Forestry Tasmania, Bob Gordon, says Gunns pulp mill won't create a need to cut down more trees.

He says there's an availability of between five to seven million tonnes of woodchips in Tasmania every year

BOB GORDON: What will happen is the pulp mill, if it's approved, will have first call on those woodchips. So, instead of exporting five to six million tonnes of woodchips, three or four million tonnes of that would go into the pulp mill and what is left over is available for woodchip export.

But the pulp mill by itself does not change any of the forest management or cutting strategies.

FELICITY OGILVIE: The Tasmanian Government's likely to make a decision to either approve or reject the pulp mill in September.

Then it's up to the Federal Government to decide if the pulp mill meets environmental guidelines.

The Wilderness Society's Geoff Law says the problem is both Governments won't be investigating what effect the mill will have on Tasmania's forests.

But the Federal Forestry Minister Senator Eric Abetz says eventually 70 per cent of the mill will be fed by plantation timber.

ERIC ABETZ: What we going to have is a lot of plantations coming online, and the future of the pulp mill proposal is in fact based on plantation forestry.